Two of the primary causes of pressure (decubitus) ulcers are pressure and moisture. Pressure results from the supporting surface resisting the force of gravity on the body. For mattresses, this pressure is typically the highest beneath the shoulder (the scapulae) and tail (the rum and trochanter), generally the areas of greatest mass and projection. Other areas subject to substantial pressure include the ankles, heel, and portions of the feet. In these high pressure areas, the pressure against the body can be sufficient to occlude the capillaries and lymph vessels, thereby preventing the circulation of oxygen and nutrients to the skin. In addition, because air flow over these skin areas is typically prevented due to the intimate contact of the surface of the mattress, greater amounts of moisture are excreted for the dissipation of heat and waste. Over a sufficient period of time, the combination of high pressure and moisture will lead to the formation of pressure ulcers.
In an effort to combat the formation of pressure ulcers among patients, hospitals utilize a number of types of bed pads for their patients who fall into high risk categories. These products include static air, water, and foam support pads. Although these pads cannot reduce the overall resistance of the mattress to the weight of the body, they can reduce the level of pressure on the areas of highest pressure by redistributing the load and allowing a greater portion of the pad to support the body. Each of these types of pads has different advantages and disadvantages.
Generally, static air and water support pads provide superior high pressure reduction capabilities at the bony protuberances, but permit only limited air flow and heat dissipation. In addition, both static air and water support pads require filling, are susceptible to leaks and tend to "bottom out" (i.e. permit the weight of the user to displace the air or water in the pad to the extent that the user is supported by the mattress, rather than by the air or water cushion). Static water support pads also are undesirable in that they are heavy and unwieldy to transport. While pumps and valves can be used to vary the pressure resistance of the static air and water pads over time, these features render the pad both expensive and difficult to install and transport.
Convoluted foam pads, on the other hand, are generally relatively inexpensive and easily transported, while providing superior air flow potential and moisture reduction capabilities. Unfortunately, despite considerable study and effort, it has proved exceedingly difficult to develop an easily manufactured convoluted foam pad which is capable of providing pressure reduction characteristics comparable to static air and water support pads.
The manufacture of convoluted foam pads continues to largely follow the methods taught by U.S. Pat. No. 3,431,802. The pads are typically formed by feeding a foam block between two cooperating parallel cylinders, each of which has an undulated surface. The cylinders rotate towards one another and are spaced so that the block inserted between them is compressed between the cylinders and is driven against a cutting edge which slices the block in half. Each half generally comprises alternating rows of peaks and valleys, in checkerboard fashion. The resulting halves are perfectly matched so that when one half is laid upon the other, the tops of the peaks of one half rest against the floor of the valleys of the other half, thus forming a solid block. In addition, although it is possible to manufacture pads which are not the mirror image or reflection of one another, this is rarely done, as it would typically result in only one usable half, thereby significantly increasing material costs.
One convoluted foam pad currently in use is disclosed in U.S. Pat. No. 4,686,724. The pad comprises alternating columns of peaks and valleys in checkerboard fashion. Air channels are stamped, press cut or laser cut through the floor of the valleys to the bottom face of the pad, leaving removable plugs used to selectively control the amount of aeration and dissipation of body heat permitted by the pad.
In one embodiment, the peaks of the pad are "topped off" to create a broken flat surface, interposed with valleys, with the distance between the floor of each valley and the bottom surface of the pad being constant. Within each valley is a channel extending from the valley floor to the flat bottom face of the pad. The patent teaches that a skin area of 1.25 inches in diameter or less, even though denied air circulation, can sustain itself from air circulating in an adjacent area. Therefore, by limiting each peak top to a diameter of 1.25 inches or less, the occurrence of pressure ulcers can, according to the patent, be virtually eliminated. Unfortunately, the use of this uniform pad with its removable plugs has found little acceptance in practice, perhaps because the removal and replacement of the individual plugs is relatively difficult and time consuming.
Thus, it would be desirable to provide an anatomically conformable support pad wherein the shoulder and tail support regions provide improved resport to their corresponding anatomical body portions in order to mitigate the occurrence of pressure ulcers and to improve comfort.